Truck frame for construction machine

Abstract

A frame for use in a construction machine such as a hydraulic excavator, in which a circle member ( 18 ) for mounting a swing circle to a center frame is secured. An outer curved portion ( 21 A) with a recessed groove shape is provided over the entire circumference in a vertically intermediate portion of the outer peripheral surface of the circle member, and an inner curved portion ( 21 B) with a recessed groove shape is provided over the entire circumference in a vertically intermediate portion of the inner peripheral surface of the circle member to thereby make it possible to render small the plate thickness (t) of the hourglass-shaped thin-walled portion ( 21 ) located in the vertically intermediate portion relative to the plate thickness (T) of upper and lower thick-walled portions ( 19, 20 ) located on both vertical end sides of the circle member. Consequently, the weight of the circle member can be reduced.

The invention claimed is:  
     
       1. A truck frame for a construction machine, said truck frame including left and right side frames and a center frame disposed between said side frames, comprising:
 said center frame being constituted by a top plate and a bottom plate which are connected to said left and right side frames at an interval in a vertical direction, a connecting tubular body provided between intermediate portions in left and right directions of said top plate and said bottom plate to connect said top plate and said bottom plate, and a cylindrical circle member which is secured to an upper surface side of said top plate and on an upper end side of which a swing circle is mounted, 
 said circle member is formed such that its upper end side is formed as an upper thick-walled portion, its lower end side is formed as a lower thick-walled portion, each of said upper and lower thick-walled portions having a same plate thickness, 
 an outer curved portion is provided in an outer peripheral surface of said circle member, said outer curved portion being located between said upper thick-walled portion and said lower thick-walled portion and formed by cutting out a recessed groove shape over an entire circumference, 
 an inner curved portion is provided in an inner peripheral surface of said circle member, said inner curved portion being located between said upper thick-walled portion and said lower thick-walled portion and is formed by cutting out a recessed groove shape over an entire circumference, and 
 a portion between said upper thick-walled portion and said lower thick-walled portion is formed as an hourglass-shaped thin-walled portion having a smaller plate thickness than the plate thickness of said upper and lower thick-walled portions and enclosed by said outer curved portion and said inner curved portion. 
 
     
     
       2. A truck frame for a construction machine according to  claim 1 , wherein each of said outer curved portion and said inner curved portion is constituted by a rectilinear portion extending rectilinearly along a center line of a plate thickness of said circle member, an upper arcuate portion connecting between said rectilinear portion and said upper thick-walled portion curvilinearly, and a lower arcuate portion connecting between said rectilinear portion and said lower thick-walled portion curvilinearly. 
     
     
       3. A truck frame for a construction machine according to  claim 1 , wherein said lower thick-walled portion of said circle member and said top plate are welded by a welding means, and a weld bead at this joint portion is formed continuously with said outer curved portion.